Fibre and film of a water-absorbent water-insoluble material having a matrix of a copolymer

ABSTRACT

Fiber or film of water-absorbent water-insoluble fibrous material has a matrix of a crosslinked copolymer formed from 50 to 95% by weight of ethylenically unsaturated carboxylic monomer and 5 to 50% by weight of copolymerisable ethylenically unsaturated monomer. The matrix contains regions of a dispersed polymeric material, the matrix copolymer and the dispersed polymeric material being mutually immiscible and chemically substantially nonreactive under ambient conditions. The fiber or film can be produced by extruding a solution or dispersion of the polymeric material in a solution of the matrix copolymer in its non-crosslinked state into a gaseous environment.

TECHNICAL FIELD

This invention relates to fibre and film of water absorbentwater-insoluble material. Water-absorbent water-insoluble materials areof use in many absorbent products, particularly products for absorbingaqueous body fluids such as baby diapers, incontinence pads, sanitarynapkins and tampons, and in wiping materials for mopping up spills ofaqueous fluids. Most water-absorbent water-insoluble materials areavailable only in powder form. There are problems in retaining anabsorbent powder in the desired position in the absorbent product, forexample in diapers. Fibre, whether staple fibre or continuous filaments,can be more effectively retained in position by incorporation in afabric, and fibre or film can also be effectively retained in positionin other products.

BACKGROUND ART

EP-A-268498 describes a water-absorbent water-insoluble polymeric fibre,film, coating, bonding layer or foam, made by forming a substantiallylinear polymer of water-soluble ethylenically unsaturated monomer blendscomprising carboxylic and hydroxylic monomers and then reacting thecarboxylic and hydroxylic monomers in the linear polymer to forminternal crosslinks within the polymer.

EP-A-269393 describes a water-absorbent water-insoluble crosslinkedpolymer fibre or film made by dry extrusion of a solution of asubstantially linear polymer formed from a water-soluble blend ofmonoethylenically unsaturated monomers comprising a plasticising monomerand evaporation of the solvent. The fibre or film is furtherplasticised, stretched and then crosslinked.

EP-A-342919 describes film or fibre made by extrusion and stretchingfrom a polymer of water-soluble ethylenically unsaturated monomers thatinclude ionic monomer. A counterionic lubricant compound is absorbedinto the surface of the fibre or film before or during the stretching.

EP-A-397410 describes a water-soluble linear polymer of carboxylic acidmonomers such as acrylic acid and a hydroxylic monomer which can becrosslinked, after being shaped by extrusion of an aqueous solution ofthe polymer as fibres or film, to form crosslinks between the carboxyland hydroxyl groups.

GB-A-2082614 describes a dry, solid, water-swellable absorbentcomprising a blend of a water-insoluble absorbent polymer, which may bea covalently crosslinked or ionically complexed anionic polyelectrolyte,and an extender material selected from the group consisting ofuncrosslinked derivatives, starch, montmorillonite clay, attapulgiteclay, seracite, talc, kaolin, silica and mixtures thereof. It statesthat the blend may be used as a film, aerated film, powder or fibre, butthere is no disclosure as to how a blend of water-insoluble polymer andextender can be made into a fibre.

DISCLOSURE OF INVENTION

According to the present invention fibre or film of a water-absorbentwater-insoluble material has a matrix of a crosslinked copolymer formedfrom 50 to 95% by weight ethylenically unsaturated carboxylic monomerand 5 to 50% by weight copolymerlsable ethylenically unsaturatedmonomer, the matrix containing regions of a dispersed polymericmaterial, the matrix copolymer and the dispersed polymeric materialbeing mutually immiscible and chemically substantially non-reactiveunder ambient conditions.

The polymeric material of the dispersed phase may be water-soluble. Thepolymeric material of the dispersed phase may be self-crosslinkable and,optionally, crosslinkable with the matrix material.

The fibre or film may be formed by extruding a solution or dispersion ofthe polymeric material in a solution of the matrix copolymer in itsnon-crosslinked state into a gaseous environment wherein solvent isremoved to form the fibre or film, and subsequently crosslinking thematrix copolymer and optionally the dispersed polymeric material.

The fibre or film may be stretched subsequent to formation, preferablybefore the crosslinking system is activated.

Although the crosslinking system can be a system that is activated byirradiation, for instance ultraviolet light, preferably it is athermally activated system, in which event the rate of crosslinking atthe temperatures prevailing during the stretching and earlier stages ofthe process should be such that there is substantially no crosslinkingduring these stages. By this means it is possible to optimise thestretching of the fibre or film while the polymer is linear and then tofix the polymer in its stretched configuration by crosslinking.

Preferably, the non-crosslinked matrix copolymer is substantiallylinear. It is formed from a blend of ethylenically unsaturated monomersthat must be selected such that the final crosslinked copolymer iswater-absorbent. Ways of selecting monomers for this purpose are known,for example from EP-A-397410 mentioned above. Generally, the blend ofethylenically unsaturated monomers is an anionic blend and usuallycomprises a carboxylic acid monomer, preferably with a non-ionicmonomer. The monomers used in the invention may be allylic but areusually vinylic, most preferably acrylic, monomers.

Preferred carboxylic monomers are methacrylic acid or acrylic acid, butmaleic acid or anhydride, iraconic acid or any of the other conventionalethylenically unsaturated carboxylic acids or anhydrides are alsosuitable. The copolymer can optionally additionally contain monomerunits derived from an ethylenically unsaturated sulphonic acid such as2-acrylamido-2-methyl-propane sulphonic acid or allyl sulphonic acid.Carboxylic and sulphonic monomer units may be present in the finalcopolymer in free acid or water-soluble salt form, suitable salts beingformed with ammonia, an amine or an alkali metal. The proportion of saltand free acid groups can be adjusted after formation of the crosslinkedcopolymer or after polymerisation of the linear polymer or beforepolymerisation. Generally, the molar ratio of free carboxylic acidgroups to alkali metal or other salt carboxylic acid groups in the finalcopolymer (and often also in the monomers that are used to form thelinear copolymer) is from 1:1 to 1:10. The ratio is usually at least 1:2and often at least 1:3. It is usually below 1:6 and often below 1:5.

When the crosslinking reaction involves reaction with the carboxylicacid groups it is usually preferred that at least some of the carboxylicacid groups should be present as free acid groups before thecrosslinking occurs. For instance, for this purpose, it may be adequatefor 10 to 75%, preferably 25 to 75%, of the acid groups to be in freeacid form before the crosslinking occurs.

Although the linear copolymer is generally made by polymerisation ofcarboxylic acid monomer (in free acid or salt form), it is also possibleto make the copolymer by polymerisation of monomer that can besubsequently reacted to form the carboxylic acid monomer. For instance,the carboxylic acid groups that are to be present (in free acid or saltform) in the crosslinked copolymer may be present initially in thelinear copolymer in the form of hydrolysable ester groups, such asmethyl ester groups, that can then be hydrolysed while in the form of alinear copolymer to yield carboxylic acid ( free acid or salt) groups.

The copolymerisable ethylenically unsaturated monomer for the matrixcopolymer may be a water-soluble ethylenically unsaturated monomer suchas acrylamide or may be a water-insoluble monomer, for example anolefin, such as isobutylene, an aromatic ethylenically unsaturatedmonomer, such as styrene or a substituted styrene, an alkyl ester ofacrylic or methacrylic acid, such as methyl or ethyl acrylate ormethacrylate, butyl acrylate or metacrylate or 2-ethylhexyl acrylate ormethacrylate, vinyl acetate or acrylontrile. One or more copolymerisablemonomers may be present. A monomer that will provide groups for internalcrosslinking with the carboxylic groups (as discussed below) is usuallyincluded. Other non-ionic monomers that may be used includeethyleneically unsaturated monomers that carry a pendent group of theformula --A_(m) B_(n) A_(p) R, where B is ethyleneoxy, n is an integerof at least 2, A is propyleneoxy or butyleneoxy, m and p are each aninteger less than n and preferably below 2 and most preferably zero, andR is a hydrophobic group containing at least 8 carbon atoms, asdescribed in more detail in EP-A-213799. The comonomer(s) are generallypresent in amounts of at least 5% and preferably at least 10% by weightbased on the monomers used for forming the copolymer, and they may bepresent in amounts up to about 50%, generally below 45%, by weight.

The substantially linear copolymer may be formed from the monomer blendin any conventional manner. It may be preformed and then dissolved toform a polymer solution. For instance, it may be made by reverse phasepolymerisation if the monomer blend is soluble in water or bywater-in-oil emulsion polymerisation if the blend is insoluble in water,e.g. at a low pH. However, this can incur the risk that the copolymermay be contaminated by surfactant and this is undesirable. Preferably,therefore, the copolymer is made by aqueous solution polymerisation orother solution polymerisation methods. It may be dried before furtherprocessing, but preferably not. Generally, it is formed by solutionpolymerisation in the solvent in which is it to be extruded (usuallywater).

The polymerisation can be conducted in conventional manner in thepresence of conventional initiators and/or chain-transfer agents to givethe desired molecular weight.

The concentration of copolymer in the solution to be extruded isgenerally in the range 5 to 50% and will be selected, having regard tothe molecular weight of the copolymer, so as to give a solution having aviscosity that is convenient for extrusion. The solution can be extrudedthrough a spinneret, suitably one of the type conventionally used insynthetic fibre production. The concentration of copolymer is usually atleast 15% by weight, with values of 30% to 45%, e.g. 35% to 40%, byweight often being particularly suitable.

The solution or dispersion that is extruded may have a viscosity as lowas, for instance, 20,000 mPa.s at 20° C., but generally the viscosity isat least 70,000 and usually at least 100,000 and sometimes at least120,000 mPa.s. It can be up to 150,000 or even 200,000 mPa.s. Highervalues are generally unnecessary. All these viscosities are measured at20° C. using a Brookfield RVT spindle 7 at 20rpm. The viscositydesirably is also relatively high at the extrusion (spinning)temperature, which typically is elevated, for instance above 80° C., butbelow the boiling point of the copolymer solution or dispersion.Preferably, the solution or dispersion at 80° C. has a viscosity of atleast 5000 or 10,000 mPa.s and most preferably at least 20,000 mPa.s.For instance, it may be in the range 50,000 to 100,000 mPa.s. Thesevalues may be obtained by extrapolation from values obtained using aBrookfield RVT viscometer spindle 7 at 20 rpm at a range of temperaturessomewhat below 80° C.

The molecular weight of the linear copolymer that is extruded may be aslow as, for instance, 50,000 or 100,000 but preferably is above 300,000and most preferably is above 500,000. For instance, it may be up to 1million or higher.

The solvent of the solution or dispersion that is extruded is usuallywater but can be methanol or other suitable organic solvent or may be ablend of water and organic solvent. The solvent must be volatile so asto permit rapid evaporation after extrusion. The gaseous environmentinto which the solution is extruded is preferably hot air. When formingfibre, the hot air can be contained in a cell of the type conventionallyused for dry spinning, or flash spinning can be used. The extruded fibrecan be taken up on conventional textile machinery, such as a godet, as ayarn or tow. A conventional spin finish, which is preferablynon-aqueous, is usually applied to the fibre before it is taken up.

When forming film, the aqueous solution or dispersion can for example beextruded via a slit die or an annular die through a heated gaseousenvironment, generally hot air, on to a support surface, for example aheated rotary drum. The support surface has release properties. Dryingof the film continues on the drum, and the film is stripped from thedrum and taken up on rolls. The moisture content of the film as it istaken up is generally in the range 8 to 25% based on the dry weight offilm, most preferably 10 to 20%.

It is preferred to stretch the fibre or film before it is collected.Stretching is effected by having the speed of the collection apparatus,for example the take-off godet, higher than the extrusion rate of thepolymer solution (the linear velocity of the polymer solution throughthe exit capillary of the spinneret or die). The ratio of the take-offspeed to the extrusion speed is generally up to 10:1 but is preferablyin the range 2-8:1, most preferably 3-6:1.

The diameter of the final fibre preferably corresponds to a weight ofbelow 20 decitex per filament, for example in the range 2 to 15 decitexper filament. This is the decitex after stretching; if stretching isused, the decitex per filament after initial extrusion may be higherthan the range quoted above. If stretching is used it is carried outbefore crosslinking.

The linear copolymer for the matrix copolymer is crosslinked afterextrusion. The crosslinking can be effected by reaction into thebackbone of the linear copolymer but preferably is by crosslinkingthrough pendent groups provided by one or more monomers that have beenpolymerised to form the linear copolymer. The crosslinking can be ionic,for instance as a result of exposing the linear copolymer to any of theknown ionic crosslinking agents, preferably polyvalent metal compoundssuch as polyvalent aluminium compounds, for example aluminium sulphate.Organic compounds may be used instead of inorganic compounds to providethe crosslinking.

Preferably, however, the crosslinking is covalent between pendent groupsin the linear copolymer.

The covalent crosslinking generally arises as a result of the formationof ester, amide (or imide) or urethane groups by reaction withcarboxylic acid groups after extruding the copolymer. Ester groups arepreferred.

The crosslinking reaction may be with an external crosslinking agent.Various systems for externally crosslinking the copolymer are describedin EP-A-269393 and these can be used in the present invention. Forexample, the carboxyl-functional linear copolymer can be crosslinked bya diisocyanate to form urethane crosslinks or by a polyamine such asethylene diamine to form amide crosslinks or by a polyfunctional reagentcontaining hydroxyl and/or epoxide groups to form ester crosslinks.

Preferably, however, the polymer is internally crosslinked by reactionbetween reactive groups within the extruded copolymer. Usually, thecarboxylic groups act as one type of reactive group and are reactivewith hydroxyl, epoxide, amino or blocked isocyanate groups. Particularlypreferred systems are described in detail in EP-A-268498. In thesesystems the extruded copolymer is formed from a monomer blend comprisingmonomer that provides carboxylic acid monomer groups and monomer thatprovides hydroxyl groups that can react with the carboxylic acid groupsto form ester crosslinks that contain only carbon and oxygen atoms inthe linkages, and these carboxylic and hydroxyl groups are reacted afterextrusion to form the said crosslinks. Generally, the carboxylic acidgroups are provided by acrylic acid or methacrylic acid and the hydroxylgroups are provided by allyl alcohol, an epoxide-substituted vinylmonomer such as glycidyl methacrylate or a hydroxyalkyl ester of a vinylcarboxylic acid such as 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate or 3-hydroxypropylmethacrylate or by vinyl alcohol groups. Alternative hydroxylgroup-containing monomers are those of the formula CHR¹ ═CR² --Y--M_(a)--OH, where R¹ is hydrogen or carboxy, R² is hydrogen or methyl, Y is O,CH₂ O or COO, M is alkyleneoxy, for example ethylenoxy or1,2-propyleneoxy, and a is an integer greater than 1 and preferably atleast 5, as disclosed in EP-A-397410. Alternatively, the comonomer cancontain a primary or secondary amine group, for example 2-aminoethylmethacrylate, which reacts to form amide crosslinks, or can contain anisocyanate group (which may need to be blocked to prevent crosslinkingduring extrusion), for example 2-isocyanatoethyl methacrylate, to formurethane crosslinks.

Reference should be made to EP-A-269393, EP-A-268498 and EP-A-397410 fora full disclosure of suitable materials and methods of extrusion and ofcrosslinking that can be used in the present invention. As stated above,heat-activated crosslinking is preferred. The temperature used tocrosslink the fibre or film can for example be in the range 150° to 250°C., with the temperatures during extrusion and stretching being lowerthan the crosslinking temperature, preferably at least 30° C. lower.

The dispersed polymeric material can for example be: starch orchemically modified starch; one or more cellulose ethers such ascarboxymethyl cellulose; polyvinyl alcohol; polyacrylamide; polyvinylpyrrolidone; a polyalkylene oxide; or a polymer of an unsaturatedsulphonic ester. The material can alternatively be a polymer of anunsaturated carboxylic ester, provided that the composition issufficiently different from the matrix copolymer to ensureimmiscibility. Under the conditions used to crosslink the matrixcopolymer the dispersed polymer may or may not also crosslink, dependingupon its chemical nature. It may be preferable for the dispersed polymerto be crosslinkable, in which case it may be preferred to incorporate alatent crosslinking agent during its preparation, for example aheat-activated crosslinking agent if the matrix copolymer is to becrosslinked by heat.

The dispersed polymeric material is preferably water-soluble. A solutionof the dispersed polymeric material in water can be prepared by directpolymerisation of one or more water-soluble monomers in water, by directdissolution of solid polymer in water, or by preparation of a latex byinverse emulsion polymerisation followed by evaporation of thenonaqueous solvent, or by chemical reaction on a slurry or latex of awater-insoluble precursor polymer. An example of such a reaction ishydrolysis of a latex of polyvinyl acetate to prepare an aqueoussolution of polyvinyl alcohol.

Prior to extrusion, it is necessary to produce a dispersion of asolution of the dispersed polymeric material in a solution of the matrixcopolymer. The dispersion is usually produced by mixing an aqueoussolution or emulsion of the polymeric material with an aqueous solutionof the matrix copolymer. The size of the dispersed polymer solutionphase should preferably be small to ensure good extrusion continuity.Mixing can be carried out mechanically, for example using a high-shearmixer, ultrasonically or by pumping the solutions through a staticmixer. It is preferable that the dispersion is extruded into fibre orfilm as soon as possible after mixing of the solutions, as the dispersedphase will increase in size with time. Dispersion agents such as blockor graft copolymers can optionally be incorporated to improve thestability of the dispersion.

The dispersed polymeric material may reduce the viscosity of thecopolymer solution or may be chosen to improve the properties of thefibre or film; for example when it is polyvinyl alcohol it may modifythe absorption and retention characteristics of the fibre or film orincrease the flexibility of the fibre or film. A natural polymer such asstarch or a chemically modified starch can be used as the dispersedpolymeric material to enhance the biodegradability of the fibre or film.

According to one aspect of the invention the dispersed polymericmaterial improves the absorbency and retention characteristics of thefibre or film for liquids. The absorbency can be measured by the freeswell test, in which 0.5 g fibre is dispersed in 30 ml aqueous liquidand left for 5 minutes. The aqueous liquid used is generally 0.9% byweight saline solution, which is generally absorbed to a similar extentto bodily fluids such as urine. The test can alternatively be carriedout with either tap water or demineralised water, but results quotedbelow are for 0.9% saline solution. For all absorbency measurements, thefibre is conditioned at 65% relative humidity and 20° C. before beingtested. The dispersion is then filtered through a sintered Mark 1 funnelof pore size 100-160 microns and is left for 5 minutes, or until itstops dripping. The water filtered through the funnel is weighed and theweight of water absorbed by the fibres is calculated by subtraction.

In an addition to the above test, the retention by the fibre or film ofthe aqueous liquid such as saline solution after application of pressureis measured by weighing the water expressed after application ofpressure at about 3.4 KPa for 5 minutes or until dripping stops.

In a further test of absorption, the absorbency under load is measuredby maintaining the fibre or film in contact with a 0.9% by weight salinesolution for an hour while applying a load of 1.7 KPa.

The presence of dispersed polymeric material in the fibre or film mayimprove the absorbency, retention or absorbency under load, as measuredby these tests, or the dryness to touch of the gel formed after thefibre or film has absorbed aqueous fluid. The dispersed polymericmaterial may also make these properties of the fibre or film lessdependent upon the concentration of ionic salts in the aqueous fluid.

The proportion of dispersed polymeric material in the fibre or film isgenerally up to 20% by weight, for example up to 15%, preferably up to10%, by weight, based on the copolymer. Usually, the proportion ofdispersed polymeric material is at least 1% by weight to achieve asignificant effect. For many purposes the proportion of dispersedpolymeric material is up to 5% by weight, and preferably at least 2%.The particle size of the dispersed polymeric material in the fibre orfilm can for example be up to about 20 or 25 microns, more usually up to15 microns. Whilst in general the size of the particles can be up toabout half the diameter of the fibre or thickness of the film, arelatively low particle size, for example less than 10 microns andpreferably less than 5 microns, is preferred when the proportion ofdispersed polymeric material in the fibre or film is above 5% by weight.A particle size of less than 1 micron may be preferred.

The polymer solution containing dispersed polymeric material is capableof being converted into fibre (including filaments and fibrils) or film(including sheet and coatings) with evaporation of the solvent aftershaping. Fibre produced can be further processed into milled fibres,chopped fibres, yarns, webs or woven, knitted or nonwoven fabrics.

The water-absorbent water-insoluble fibre or film of the presentinvention can be used in various products. It can, for example, be usedin absorbent personal products such as tampons, disposable diapers,sanitary napkins or incontinence pads. The absorbent fibre is preferablyused in combination with other fibres, for example cellulosic fibressuch as cotton or regenerated cellulose fibres, including multi-limbedcellulose fibres as described in EP-A-301874, or polypropylene orpolyester fibres. The absorbent fibre can be intimately mixed with saidother fibres, for example by carding or air-laying the fibres togetherto form a web of mixed fibres. Alternatively, the absorbent fibre orfilm can be used as a layer, for example a non-woven fabric of absorbentfibre, sandwiched between layers of other fibres. The proportion ofabsorbent fibre in a blend with cellulosic fibres for absorbent productscan for example be at least 5% and up to 95%, preferably at least 10%and up to 50%, by weight. The absorbent fibre can also be used atsimilar levels in conjunction with fluffed wood pulp or synthetic fibrepulp, for example polyolefin pulp, in absorbent products.

A yarn, woven fabric or nonwoven fabric comprising the absorbent fibrecan be used as a swellable material which prevents ingress of water inunderground cables. A yarn or fabric tape or an absorbent film can beused to wrap cable or can be laid longitudinally in the cable.

The absorbent fibre or film can be used in many other applications ofthe types described in Research Disclosure, January 1992 at pages 60-61,for example in filters, absorbent liners or mats for packaging,disposable wipes, mats, shoe insoles or bed sheets, swellable gaskets orseals, moisture-retention mats in horticulture, moisture-retainingpackaging or swellable self-sealing stitching threads.

The invention is illustrated by the following Examples:

Example 1

A 40% by weight solution of "Goshenol GL05" (Trade Mark) poly(vinylalcohol) was prepared at 70° C. This solution was added to a 38% byweight aqueous solution of a copolymer of 78 mole % acrylic acid (75%neutralised as sodium salt), 20 mole % methyl acrylate and 2 mole %hexapropylene glycol monomethacrylate. The suspension was added at 55°to 65° C. and stirred with a paddle stirrer. After 2 hours an evendispersion was obtained, containing approximately 38% by weight solidsand 2% by weight polyvinyl alcohol based on total polymer.

This dispersion was spun into filaments through a spinneret into a cellwhere water was evaporated from the filaments. The temperature of thedispersion at the spinneret was between 90° and 100° C. The cell washeated by tube wall heaters at 150° C. The filaments were taken up atapproximately 200 m/min to give a fibre of approximately 15 dtex.Samples of the resulting multifilament tow were crosslinked by heatingin air under the conditions shown in Table 1. The free swell absorbency,retention and absorbency under load (AUL) of the resulting fibres weremeasured in each case by the methods described above.

                  TABLE 1                                                         ______________________________________                                        Crosslink                                                                     time at   Free Swell    Retention                                                                              AUL                                          210° C.                                                                          g/g           g/g      g/g                                          ______________________________________                                         6 mins   49.2          32.2     26.8                                          8 mins   46.2          31.7     24.2                                         10 mins   39.3          24.9     21.5                                         12 mins   39.8          25.2     23.8                                         ______________________________________                                    

The results indicate that the fibres have a relatively high absorbencyunder load. At all degrees of crosslinking the absorbency under load ofthe fibres tested was higher than that of similar fibres containing nopolyvinyl alcohol which had an equally high free swell absorbency. Thefibres appeared more flexible than similar fibres containing nopolyvinyl alcohol.

Example 2

Starch was dissolved in water and mixed with a solution in water of acopolymer of acrylic acid, methyl acrylate and hexapropylene glycolmonomethylacrylate in the ratio 60:35:5 by weight to produce a 38% byweight dispersion containing 5% by weight starch based on total polymer.The conditions of mixing were as described in Example 1. The dispersionproduced was dry spun as described in Example 1. The spun filaments werecrosslinked at 200° C. for 10 minutes to produce superabsorbentfilaments. The water absorbency and retention of the filaments weresimilar to those of similar filaments without the starch, and thefilaments of Example 2 had enhanced biodegradability.

We claim:
 1. Fibre or film of a water-absorbent water-insoluble materialhaving a matrix of a crosslinked copolymer formed from 50 to 95 % byweight of ethylenically unsaturated carboxylic monomer and 5 to 50% byweight of copolymerisable ethylenically unsaturated monomer, the matrixcontaining regions of a dispersed polymeric material, the matrixcopolymer and the dispersed polymeric material being mutually immiscibleand chemically substantially non-reactive under ambient conditions. 2.Fibre or film according to claim 1, wherein the dispersed polymericmaterial is a water-soluble polymer.
 3. Fibre or film according to claim1, wherein the dispersed polymeric material is crosslinked.
 4. Fibre orfilm according to claim 1, wherein the dispersed polymeric material isstarch or a chemically modified starch and the fibre or film hasenhanced biodegradabllity compared to fibre or film formed of the matrixcopolymer alone.
 5. Fibre or film according to claim 1 wherein thedispersed polymeric material is polyvinyl alcohol and the fibre or filmhas increased absorbency under load and/or increased flexibilitycompared to fibre or film formed of the matrix copolymer alone.
 6. Fibreor film according to claim 1 wherein the dispersed polymeric material isa cellulose ether, a polyalkylene oxide or a polymer of an unsaturatedsulphonic ester.
 7. Fibre or film according to claim 1 wherein thedispersed polymeric material is present at 1 to 10% of the dry weight ofthe fibre or film.
 8. Fibre or film according to claim 7, wherein thedispersed polymeric material is present at up to 5% of the dry weight ofthe fibre or film.
 9. Fibre or film according to claim 1 wherein thematrix copolymer is crosslinked by ester crosslinks.
 10. Fibre or filmaccording to claim 9, wherein the copolymerisable ethylenicallyunsaturated monomer of the matrix copolymer consists at least partly ofa hydroxyl-functional or epoxide-functional comonomer, and that theester crosslinks are formed by reaction between carboxylic acid groupsderived from the carboxylic monomer and hydroxyl or epoxide groupsderived from the copolymerisable monomer.
 11. A process for theproduction of fibre or film of a water-absorbent water-insolublematerial having a matrix of a crosslinked copolymer formed from 50 to95% by weight of ethylenically unsaturated carboxylic monomer and 5 to50% by weight of copolymerisable ethylenically unsaturated monomer, the.matrix containing regions of a dispersed polymeric material, the matrixcopolymer and the dispersed polymeric material being mutually immiscibleand chemically substantialially non-reactive under ambient conditions,wherein a solution or dispersion of the polymeric material in a solutionof the matrix copolymer in its non-crosslinked state is extruded into agaseous environment wherein solvent is removed to form the fibre orfilm, and the matrix copolymer, and optionally the dispersed polymericmaterial, is subsequently crosslinked.
 12. A process according to claim11, wherein the solution of the matrix copolymer is an aqueous solution.13. A process according to claim 12, wherein the concentration of thematrix copolymer in the aqueous solution is 30 to 45% by weight.
 14. Aprocess according to claim 11, wherein the solution or dispersion isextruded at a temperature which is above 80° C. but below the boilingpoint of the copolymer solution or dispersion.
 15. A process accordingto claim 11, wherein the solution or dispersion has a viscosity at 80°C. of at least 20,000 mPa.s.
 16. A process according to claim 11,wherein the solution or dispersion is extruded through a spinneret toform fibres.
 17. A process according to claim 11, wherein thecrosslinking is effected by heating the fibre or film at a temperaturein the range 150° to 250° C.
 18. A process according to claim 11,wherein the fibre or film is stretched before effecting the crosslinkingof the copolymer.